The present invention extends to methods, systems, and computer program products for detecting hazards in anticipation of opening vehicle doors. Vehicle sensors (e.g., rear viewing cameras) can be used to detect and classify traffic, for example, as pedestrians, bicyclists, skateboarders, roller skaters, wheel chair, etc., approaching on the side of a vehicle. When there is a possibility of a vehicle occupant opening a door into approaching traffic, a warning can be issued in the vehicle cabin to alert vehicle occupants of the approaching traffic. In one aspect, a vehicle prevents a door fromopening if opening the door would likely cause an accident.